System CPU Usage View

Function:

• To display overall system CPU usage statistics.

Description:

• This view displays a horizontal bar graph depicting the operating system CPU usage, user CPU usage, and idle times. The idle time is divided between completely idle time and idle time due to the system waiting for disk I/O to complete.

• Os CPU usage is the relative time spent inside the operating system, executing services on behalf of user programs. User CPU time is the time spent executing the user programs. When the system has no processes that are runnable, the system is said to be idle. Time spent by processes waiting for disk I/O requests to be satisfied is represented by the wait_disk value.

• A system that has a high waiting for disk I/O value indicates a system that is I/O bound. You can examine the Process I/O View to determine which processes are responsible for the I/O load. A system that has a very low idle or waiting for disk time may be experiencing a CPU bottleneck. Brief periods of no idle time are normal in any system, after all, you want the system to use every available resource to complete your desired tasks as quickly as possible. However if this persists, new programs will not load or run in an acceptable manner. In such cases, you can examine the Process CPU View to determine which processes are responsible for the CPU load.

• A CPU bottleneck exists if the low idle condition persists over a period of several minutes. Invoke the Format, Instance menu option to select the average mode of display. You can then select the Format, Reset Average option to recommence average calculations. Recheck the idle CPU statistics after several minutes to determine if you have a CPU bottleneck. The historical database may also be consulted to see when the bottleneck was first introduced to the system.

• An ideal system should exhibit a reasonable balance between system CPU usage and user CPU usage. Excessive system CPU load can be caused by many factors, most of which are problematic. Some of the most common are:
  • Faulty network hardware generating continual device interrupts.

  • Very large directories causing excessive scanning when opening files.

  • Poorly written applications that make redundant or excessive system calls.